how to draw an arrow object or a line object in the scene?

[humorstar]

I am trying to add a line which connects two objects, and an arrow pointing away from an object in the scene.

Do I have to create a scene node for an arrow or line? Such as creating an ArrowSceneNode?
Or can I use OpenGL to directly draw some lines there? It doesn't look I can use OpenGL to draw directly. No complaint when compiling but I see no opengl graphics output.

[hybrid]

You can simply use the arrowmesh provided by Irrlicht, and render it using a mesh scene node.

[humorstar]

You can simply use the arrowmesh provided by Irrlicht, and render it using a mesh scene node.

Thank you for the reply. Where is this arrowmesh? I did not see it under the \media folder. I need to dynamically change the size of arrow or line. Is that possible?

[SwitchCase]

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IAnimatedMesh* arrowMesh = smgr->addArrowMesh ("arrowMesh");

There are serveral ways of making a scene node of the mesh one way is:

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IAnimatedSceneNode* arrowNode = smgr->addAnimatedMeshSceneNode (arrowMesh);

another way is:

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ISceneNode* arrowNode = smgr->addSceneNode ("arrowMesh");

There are extra parameters, default values are used if you don't pass these member functions some parameters, the only essential ones are the first though. - look in the Irrlicht documentation in the 'irrlicht/docs/' folder. A search for "arrow mesh" sends you to irr::scene::ISceneManager Class Reference where you'll find what you need.


As for changing the size of the arrow:

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arrowNode->setScale (vector3df(x value, y value, z value) );

You need to look in the documentation when you have questions like this in the future. And i'm sure by doing this you'll also be able to find out about drawing lines.

[humorstar]

Thank you for the help. I am trying to convert a direction vector, i.e., a vector pointing from one point to another, to a 'rotation' matrix, so that I can assign this rotation matrix to the arrowMesh. How to do it properly?

I am a bit confused by the coordinate system of Irrlicht. Is it a left-hand system?

Thanks again,

[SwitchCase]

Why do you need a matrix? Simply give the scenenode rotation setter function your vector.

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sceneNode->setRotation ( yourVector );

Where your vector is of type irr::core::vector3df

[rogerborg]

I think what humorstar may be wanting is something like this:

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#include "irrlicht.h"

using namespace irr;
using namespace core;
using namespace scene;
using namespace video;

#ifdef _IRR_WINDOWS_
#pragma comment(lib, "Irrlicht.lib")
#endif

int main()
{
	IrrlichtDevice *device = createDevice( EDT_OPENGL,
								 dimension2d<s32>(800, 600),
								 32);
	ISceneManager* smgr  = device->getSceneManager();
	IVideoDriver* driver = device->getVideoDriver();

	(void)smgr->addCameraSceneNode();

	IBillboardSceneNode * bill = smgr->addBillboardSceneNode();
	bill->setMaterialType(video::EMT_SOLID );
	bill->setMaterialTexture(0, driver->getTexture("../../media/wall.bmp"));
	bill->setMaterialFlag(video::EMF_LIGHTING, false);

	ISceneNodeAnimator * animator = smgr->createFlyCircleAnimator(vector3df(0, 0, 100), 40.f, 0.005f, vector3df(1, 1, 1).normalize());
	bill->addAnimator(animator);
	animator->drop();

	// The arrow mesh points towards +Y, but getHorizontalAngle() assumes +Z
	// so we'll use a parent node to rotate the arrow mesh node by 90 degrees.
	ISceneNode * arrowParent = smgr->addEmptySceneNode();
	arrowParent->setPosition(vector3df(0, 0, 100));
	ISceneNode * arrow = smgr->addAnimatedMeshSceneNode(smgr->addArrowMesh("arrow", 
				SColor(255, 255, 0, 0), SColor(255, 0, 255, 0)), arrowParent);
	arrow->setMaterialFlag(video::EMF_LIGHTING, false);
	arrow->setRotation(vector3df(90, 0, 0));
	arrow->setScale(vector3df(20, 20, 20));

	while (device->run())
	{
		driver->beginScene(true, true, video::SColor(0,100,100,100));
		smgr->drawAll();
		driver->endScene();

		const vector3df toBillboard = (bill->getAbsolutePosition() - arrow->getAbsolutePosition()).normalize();
		const vector3df rotations = toBillboard.getHorizontalAngle();
		arrowParent->setRotation(rotations);
	}
}

[humorstar]

Yes, this is exactly what I am looking for. Your program, when compiled with irrlicht 1.4.2, needs a minor change:
const vector3df toBillboard
to
vector3df toBillboard

Otherwise it is all right to compile. Thank you very much,

[rogerborg]

Ah, right, getHorizontalAngle() wasn't made const until after 1.4.2. Happy to help.